ABSTRACT
Pectin methylesterase (PME) hydrolyzes methyl ester groups in pectin chains to form carboxylic groups, releasing methanol and H3O+. The aim of this study was to determine PME activity in samples of pectinases by UV-VIS spectroscopy, to measure the acid and methanol produced in the reaction of pectin with pectinase and to verify the thermal inactivation of exogenous PME in mango juice. The activity of PME in samples of pectinase was determined by potentiometry, UV-VIS spectroscopy, and by the action of alcohol oxidase. The reaction showed greater activity at pH 4.0 to 4.5 and at a temperature of 45° C. PME activity determined by UV-VIS spectroscopy with bromophenol blue indicator showed a good correlation with the activity determined by potentiometry and with alcohol oxidase. The results showed that bromophenol blue indicators can be used to determine PME activity in samples of pectinases where the optimum pH is located in the acidic range. The thermal inactivation of exogenous PME in mango juice occurred at 75° C for 20 min of exposure.
A PME hidrolisa os grupos metil éster na cadeia da pectina, formando grupos carboxílicos, liberando metanol e H3O+. Objetivou-se, com o presente estudo, determinar a atividade da PME em amostras de pectinases por espectroscopia Uv-vis para quantificar o ácido e o metanol produzido na reação da pectina com as pectinases e verificar a inativação térmica da PME exógena no suco de manga. A atividade da PME nas três amostras de pectinases foi determinada por potenciometria, espectroscopia Uv-Vis, e pela ação da álcool oxidase. A reação mostrou uma maior atividade em H de 4,0 a 4,5 e a temperatura de 45º C. A atividade da PME, determinada por UV-Vis com o indicador azul de bromofenol apresentou uma boa correlação com a atividade determinada por potenciometria e com a álcool oxidase. Os resultados mostraram que o indicador azul de bromofenol pode ser utilizado para determinar a atividade da PME em amostras de pectinases em que o pH ótimo situa-se na faixa ácida. A inativação térmica da PME no suco de manga ocorreu na temperatura de 75º C, por 20 min de exposição.
ABSTRACT
In this work, glucoamylase was produced by Aspergillus niger in solid-state fermentation. The enzyme was partially purified by ammonium sulphate precipitation and ion exchange and gel filtration chromatographies. Its molecular mass was estimated as 118.17 kDa by electrophoresis. The partially purified enzyme had an optimum pH range of 4.5-5.0 and an optimum temperature of 60 °C, with average activity 152.85 U mL-1. Thermal and pH stability assays with the crude extract showed that more than 60 percent of the activity remained at pH 4.6 and 60 °C, even after an exposition to these conditions longer than 24 h. Yet, after purification, the enzyme was stable at these for at least 4 h, which indicated that its purification for use in starch saccharification was inadvisable. K M and Vmax were 0.34 mg mL-1 and 160.22 U mL-1, respectively.
ABSTRACT
Bee (Apis mellifera L.) honeys have been widely used for therapeutic and nutritional proposes. For evaluating the honey production, physicochemical approaches have been extensively performed to ensure that this hive product is authentic in respect to the legal requirements. The aim of this paper was to discuss the quality control of 93 samples of honey from Campos Gerais region of Paraná State South Brazil by physicochemical parameters. Moisture, reducing sugars, sucrose, water-insoluble solids, ash, free acidity, pH, activity of diastase, hydroxymethylfurfural content and colour were performed by the standard usual methods. Samples were also classified in floral honeys or honeydew honeys according to the Kirkwood equation. A total of 71 samples (76.34%) showed values in accordance with the Brazilian legal requirements for all the achieved physicochemical parameters. Otherwise, all the studied honeys were likewise within the legislation limits only for water-insoluble solids and colour. For pH, an additional parameter that has not been provided in honey legislation, samples showed values ranging from 3.60 to 5.35. By the Kirkwood equation, 61 honeys were considered as floral products.